In late September Turkey's private Dogan news agency reported that a six-vehicle convoy moved three Howitzers and an anti-aircraft gun to the border as shells from Syria began landing in Turkish towns near the border.

A Howitzer is a large gun that fires heavy shells, relatively short distances, at pretty steep angles. Howitzer shells come in many different varieties, but are commonly highly explosive.

Turkey's state-run Anatolia news agency reports that the military deployed additional tanks and missile defense systems to the Syrian border on Sunday. Last week Turkey's parliament authorized sending troops across the border.

Bloombergreports that Turkish Foreign Minister Ahmet Davutoglu told state-run television on Oct. 6 that the five civilian deaths in a Turkish border town on Oct. 3 were caused by a D30 type, 122mm artillery shell, which is used by the Syrian army. (A Turkish newspaper reported that it was a NATO mortar.)

To give you an idea of what goes into firing these things, here's the Afghan National Army firing a 122mm Howitzer.

And to provide an idea of what this type of shell can do, here's a video of U.S. combat engineers destroying a 122 mm artillery round in Iraq—the shrapnel actually hits their Humvee:

A Turkish newspaper Milliyet speculated that Turkish F-16 warplanes may strike Syrian artillery batteries if Syrian shells cause new casualties, according to Bloomberg.